Disk control unit and storage system

ABSTRACT

A disk controller has a front end FC I/F to a host, a back end FC I/F to a magnetic disk, a processor, and a main memory section. The front end I/F and the back end I/F are provided for performing information exchange with a network (connected) device that is connected to a network and manages storage. The main memory section stores registered information expressing an attribution of the network (connected) device, access information including the security and the performance of each network (connected) device through the network, and ranking information assigning a rank to each network (connected) device based on the registered information and the access information. An appropriate network (connected) device is selected from various types of information including the ranking information.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2004-082824, filed on Mar. 22, 2004, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a storage system and to a managementmethod for such a storage system, the storage system having a diskcontroller and an iSCSI device connected to the disk controller by anetwork. More particularly, the present invention relates to a formatfor managing storage connections on the network.

As IT becomes more widespread and entrenched, users continue to seekgreater data storage capacity. Because of this, there are many caseswhere more data storage is necessary than the capacity originallyinstalled in a storage system.

FIG. 8 shows an example of the overall construction of a conventionaldisk controller and storage system. In the conventional system shown inFIG. 8, a management program 235 on an SVP (Service Processor) 230responds to an operation input to issue an instruction to a controlprogram 217 and to a device list 218 located inside a disk controller210 to register a new storage as a storage to be governed by the diskcontroller 210 itself and to connect a corresponding new magnetic disk220 to a back end FC I/F 213, thereby achieving extension of the storagecapacity.

In another method for increasing the storage capacity, instead of themagnetic disk 220, FC heterogeneous storage 227 having an FC device 225is connected. Here, the term “storage” refers collectively to magneticdisks, magnetic tape, etc. The term “Heterogeneous storage” refers toany storage medium that the disk controller does not manage directly.Also, “FC” is an abbreviation for Fiber Channel. An example of an FCstorage system is illustrated in an IBM white paper called “IBM StorageTank™, A Distributed Storage System”, dated Jan. 24, 2002.

As shown in FIG. 8, when making a remote copy or effecting a backup ofdata, the storage where the remote copy is to be made does notnecessarily have to be recognized by the disk controller as a storagegoverned by the disk controller 210 itself. Therefore, it is alsopossible to use a SAN (Storage Area Network) 250 to connect aheterogeneous storage 229 to a front end FC I/F 212 via an FC device260. An example of such a construction is disclosed in U.S. Pat. No.6,092,066.

On the other hand, in an IP network, transmissions can only be performedin accordance with TCP/IP protocol, for example. Therefore, in order todirectly send SCSI protocol, which is common for a disk unit I/O, to thedisk unit, a new protocol is necessary to piggyback common SCSI commandsand the like onto the data portion of an IP frame. A representativeexample of this new protocol is iSCSI protocol.

An example of a storage system using iSCSI is disclosed in U.S. Pat. No.5,996,024. This type of iSCSI I/F can transmit information about amagnetic disk, which is a target, to the disk controller, which is aninitiator.

In a storage system using the FC I/F as described above, the network isclosed inside the disk controller. Therefore, since it is possible tolearn the status of everything, including the status of the FCheterogeneous storage and the status along the route thereto, it ispossible to select the optimum storage when recording data.

However, in the FC I/F storage system described above, it is notpossible to connect an IP network and an iSCSI heterogeneous storagethat are spread widely around the world. Therefore, in order to create anetwork on an IP-network scale, it is necessary to set up a separatenetwork with just the FCs. Furthermore, management methods used on IPnetworks cannot be simply transferred and used on a storage system usingthe FC I/F described above.

In order to add more storage using the FCs and a SAN, as disclosed inU.S. Pat. No. 6,092,066, it is necessary to establish the SAN networkseparately from the general IP network. This creates problems ofincreased equipment costs and management costs.

On the other hand, with an iSCSI I/F using an IP network, the iSCSIstorage can be connected as the target, but only information about thetarget can be transmitted. Therefore, it is not possible to obtaininformation about the performance of the network leading to the iSCSIstorage, or information about security, costs, or other such informationabout the IP network. Therefore, there is a problem in that it has notbeen possible to connect optimally to an iSCSI heterogeneous storage ina way which takes the status of the network into consideration.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the present inventionadopts mainly the following construction.

In a disk control unit comprising a front end FC I/F, which is aninterface to a host, a back end FC I/F, which is an interface to amagnetic disk, a processor for controlling each section, and a mainmemory section a front end I/F and a back end I/F are provided toexchange information with network (connected) devices that are connectedto a network and to manage data storage. The main memory section storesregistered information expressing an attribution of the network(connected) devices, access information including information aboutsecurity and the performance of each network (connected) device throughthe network, and ranking information assigning a rank to each network(connected) device based on the registered information and the accessinformation; and, an appropriate network (connected) device is selectedfrom various types of information, including the ranking informationstored in the main memory section, based on a condition requested by thecomputer.

In the disk control unit, communication with the network (connected)devices uses iSCSI protocol or IP protocol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the overall constructionof Embodiment 1 of a disk controller and a storage system in accordancewith the present invention;

FIG. 2 is a diagram of a device list of a device control unit inaccordance with Embodiment 1;

FIG. 3 is a flow chart showing an example of device registration,testing, updating and accessing between the disk controller and an iSCSIdevice in accordance with Embodiment 1;

FIG. 4 is a diagram showing a flowchart of device registration, testing,updating and accessing by a storage broker device inside the diskcontroller in accordance with Embodiment 1;

FIG. 5 is a diagram showing a flowchart of iSCSI device registration,test reporting and a device list change, in accordance with Embodiment1;

FIG. 6 is a block diagram showing an example of mirroring, backing upand storage of system log data by the disk controller in accordance withEmbodiment 1;

FIG. 7 is a flowchart showing an example of device registration,testing, updating and accessing between a disk controller and an iSCSIdevice in accordance with an Embodiment 2 of the present invention; and

FIG. 8 is a block diagram showing the overall construction of a diskcontroller and storage system in accordance with a conventional example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a disk controller of the present invention will beexplained in detail below, with reference to Embodiment 1 and Embodiment2 as examples.

FIG. 1 is a diagram showing the overall construction of Embodiment 1 ofa disk controller and a storage system. In FIG. 1, a host 1 (100) and ahost 2 (101) are connected to a disk controller 110 via a front end FCI/F 111, and they can read and write data using the FC protocol. Thedisk controller 110 controls data between the computer (below, “host”)100 and the host 2 (101) and a magnetic disk 120. Furthermore, insidethe disk controller 110, there is provided a front end iSCSI I/F 112,which is an interface to IP networks 150, 151, 152. Here, the front endiSCSI I/F 112 is used, for example, as an interface to heterogeneousstorage (any storage which is not directly managed by the diskcontroller) for making a remote copy or a backup of data.

The disk controller 110 has a back end FC I/F 113 as an interface to themagnetic disk 120, and the magnetic disk 120 is connected to the backend FC I/F 113. Furthermore, the disk controller 110 has a back endiSCSI I/F 114 and is connected to a magnetic disk 121, and the magneticdisk 121 is managed directly. Furthermore, the disk controller 110 hasthe back end iSCSI I/F 114 as an interface to iSCSI devices 160, 170 onthe network, which are external devices connected via the networks 150,151, 152. In other words, a router 140 or the iSCSI devices 160, 170 areconnected to the backend iSCSI I/F 114 as devices on the network. Here,the router 140 may also be a network switch.

Furthermore, the iSCSI devices 160, 170 are connected to the front endiSCSI I/F 112 inside the disk controller 110 via the router 14 and thenetworks 150, 151, 152. Information is exchanged between the front endand the iSCSI devices. Furthermore, a cache memory 119 is provided alongthe route where the data is transferred from the front end FC I/F 111 tothe back end FC I/F 113. The cache memory is used for high-speed dataaccess.

The entire disk controller 110 is controlled by a control processor 115.Programs, tables, lists, etc. are stored in a main memory 116.Furthermore, in order to enable structural changes, monitoring,controls, etc. to be made to the disk controller 110 from an externallocation, the disk controller 110 is provided with a SVP (serviceprocessor) 130 containing a management program 135. The SVP is connectedto the control processor 115. The SVP 130 may be subordinate to the diskcontroller 110 and perform the functions of a personal computer. In thiscase, a user can give instructions to the control processor 115 byperforming input operations on the SVP 130. Furthermore, the SVP 130 maybe connected to the disk controller 110 via a network and performfunctions similar to the hosts. Among the programs stored in the mainmemory 116, there is a storage broker 117 as a program according to thepresent invention. This program performs control of the iSCSI devices.Moreover, the main memory 116 has a device list 118 serving as adatabase storing information that is necessary when connecting to theiSCSI devices 160, 170.

The front end iSCSI I/F 112 and the back end iSCSI I/F 114 are connectedvia the router 140 to the networks 150, 151, 152, and the router 140sends IP packets from each interface to the networks 150, 151, 152 insuch a manner as correctly corresponds to the addresses of the IPpackets. On the other hand, the iSCSI devices 160, 170 are connected tothe networks 150, 151, 152. Inside the iSCSI devices 160, 170 there arestorage broker replying (micro) programs 165, 175 as programs forexchanging information with the storage broker 117.

The storage connected to the iSCSI devices 160, 170 includes, forexample, an iSCSI heterogeneous storage 167 and a heterogeneous magnetictape disk 125 and the like, which are not directly managed by the diskcontroller 110. Thus, by connecting the disk controller 110 and theiSCSI heterogeneous storage 167 and the like, it becomes possible tofreely add voluminous storage beyond the capacity of the FC I/F magneticdisk 120 that is under the direct management of the disk controller 110.

Furthermore, for information about the networks 150, 151, 152 (e.g.,their performance, security, cost, etc.) it is possible to useinformation stored in the router 140. This information can be utilizedby applying the protocol that is normally used. SNMP is one example.Information about the iSCSI devices 160, 170 can be collected duringnegotiation and other procedures performed during iSCSI Loginprocessing. The ranking of the iSCSI devices 160, 170 will be explainedbelow, using the device list shown in FIG. 2.

Here, the device registration, deletion, test accessing andtransmission/reception of data that the storage broker 117 of the diskcontroller 110 performs over the network with the storage brokerreplying (micro) programs 165, 175 in the iSCSI devices 160, 170 areperformed via the front end iSCSI I/F 112 or the back end iSCSI I/F 114.That is, based on an instruction from the control processor 115 thatcontrols the overall disk controller 110, the storage broker 117 sends adevice registration request and the like (see step 400 in FIG. 3described below) through the front end iSCSI I/F 112 or the back endiSCSI I/F 114 to the iSCSI devices 160, 170.

Methods for the control processor 115 to manage the iSCSI devices 160,170 on the network include: a first method, in which the controlprocessor 115 manages everything just like the magnetic disk 121 whichthe control processor 115 itself governs, or a second method, in whichthe management is yielded to the iSCSI device. If the first method isused, the control processor itself manages the iSCSI devices 160, 170 onthe network, so that data distribution and other detailed controlsbecome possible. If the second method is used, the control processoryields the data management to the iSCSI devices on the network, and thusit becomes possible to reduce the control processor's managementoverhead. Whether to use the first method or the second method may bedetermined by the control processor based on it's own load, or by aninstruction from the SVP by the user.

Here, the device registration, deletion, test accessing andtransmission/reception of data that the storage broker 117 performs withthe storage broker replying (micro) programs 165, 175 of the iSCSIdevices 160, 170 on the network are executed according to controls bythe control processor 115. However, the control processor can use eitherthe front end iSCSI I/F 112 or the back end iSCSI I/F 114 to execute theregistration, etc. Basically, it is not necessary to distinguish betweenusage of the front end I/F and the back end I/F, so either end I/F maybe used. In a typical example of usage, for backing up and for remotecopying, the control processor may perform controls so that the frontend I/F is used. For adding disks (this is a process that enables thedisk controller to use heterogeneous storage present broadly through theIP network) controls may be performed to use the back end I/F (adding amagnetic disk to be managed directly by the control processor is similarto the normal processing method using the back end I/F.) Furthermore,whether to use the front end I/F or the back end I/F may be determinedby the control processor according to an instruction from the SVP madeby the user.

As shown in FIG. 1, each of the iSCSI devices 160, 170 can be connectedto each of the networks 150, 151, 152 as a way to deal with a case wherean accident occurs on one of the networks. In FIG. 1, the X mark on theconnection line between the network and the iSCSI device indicates anetwork accident. Also, in FIG. 1, in response to the data write requestfrom the host, the disk controller 110 generally selects the magneticdisks 120, 121 that are directly managed by the disk controller, but inthe case of a request to write voluminous data that cannot all be storedon the magnetic disks 120, 121, or in a case where the capacity of emptyspace on the magnetic disks 120, 121 has become small, or in a casewhere copy data is to be stored onto a storage medium other than themagnetic disks 120, 121, the data is written onto the externalheterogeneous storage or heterogeneous storage medium via the network.

FIG. 2 is a structural diagram of a device list according to Embodiment1 of the disk controller. In FIG. 2, Rank 310 indicates a priority levelwith which a new connection will be made to each registered iSCSI deviceon the network in response to a request from the host or the SVP.iSCSI-Name 320 indicates an address of each iSCSI device. Capacity ofEmpty area 330 indicates usable data capacity in each iSCSI device.Transfer Speed or Delay 340 indicates a data transfer speed or amount oftime required to transfer data, which should be expected when accessingeach of the iSCSI devices.

Furthermore, in the device list 118, Security 350 indicates the safetyof the routes from the iSCSI devices 160, 170 to the disk controller110, as determined based on the number of incidences that have occurredthere in the past, the security configured there, etc. Running orResting 360 indicates the current running state of each iSCSI device160, 170. Cost 370 indicates the cost necessary to use each iSCSI device160, 170.

Using each of these entries, the storage broker 117 determines the rankof each of the registered iSCSI devices 160, 170 as relevant to acondition requested by the disk controller 110. Here, the requestedcondition may be, for example, a condition requiring that voluminouswriting is necessary, a condition requiring that the data to be handledis important or confidential, or a condition requiring that the diskcontroller itself has detected and learned its own load status, forexample, such as how fast or slow its transfer speed is, or the volumethat is too large to write, etc.

An example of a way to determine the rank is to assign ranks to theentries from 320 to 370 for each device, and then, based on thecondition requested by the disk controller 110, assign weight to thoseentries which are considered important, and then total these up tocalculate the ultimate rank. A specific method for assigning the rankscould be, for example, to numerically express (standardize) those whichcan be numerically expressed as “Xij” (where “i” represents the devicenames written vertically in FIG. 2, and “j” represents the entrieswritten horizontally in FIG. 2), and then multiply these by weights W1,W2, W3, . . . Wi provided by the SVP 130 (where a greater value of “Wi”indicates greater importance), and then assign the ranks according tothe size of the value (Rank-i) thus produced.Rank1=W 1×X 11+W 2×X 12+W 3×X 13+ . . .Rank2=W 1×X 21+W 2×X 22+W 3×X 23+ . . .

There is also a method for expressing those which cannot be numericallyexpressed as rules (such as whether the device is running or resting).For example, the rule may be expressed as “if i=running, then Rank-i=R1;else Rank-i=0 (where R1 is a value determined in advance)”.

Furthermore, since the SVP 130 is connected via the router 140 and thenetworks 150, 151, 152 to each of the iSCSI devices and thus hasconnections similar to the control processor 115, the SVP 130 can alsoperform the ranking of each of the registered iSCSI devices similar tohow ranking is performed by the control processor 115, as describedabove. The results of the ranking are stored in the device list 118 viathe control processor. Note that it is self-evident that the user canadd entries that are necessary besides those shown in FIG. 2.

FIG. 3 is a flow chart showing an example of device registration,testing, updating and accessing between the disk controller and theiSCSI device on the network in accordance with Embodiment 1. In FIG. 3,first, a device registration start command is transmitted from one ofthe hosts 100, 101 or the SVP 130 to the disk controller 110 (405). Thecontrol processor 115 of the disk controller 110 issues an iSCSI deviceregistration request to the network's iSCSI devices 160, 170 and storagebroker replying (micro) programs 165, 175 (400). The iSCSI devices 160,170 that received the request then register their own device information(410). Next, based on controls by the control processor 115, the storagebroker 117 registers the iSCSI device(s) that replied into the devicelist 118 (420).

Then, the storage broker 117 assigns ranks to the information of theregistered iSCSI devices (430). Furthermore, the storage broker 117performs a test access to the registered iSCSI devices(s) or the router140 that is en route thereto, and collects information about the networkstatus, etc. (440).

The router 140 or iSCSI devices 160, 170 on which the test access wasperformed then reply to the test access (450). If the iSCSI devices 160,170 have had their own device information (e.g., their capacity of emptyarea, etc.) updated, they register the change in information with thestorage broker 117 (455). Once registration of the information isfinished, the storage broker 117 assigns ranks to the iSCSI deviceinformation once again (460).

After that, when a device request to add a device or create a journallog or perform a backup or a remote copy is sent to the storage broker117 from an external location (e.g., the host or SVP) (470), aconnection is then established to the iSCSI device with the highest rankand this device is registered (475). When this registration isperformed, the registered iSCSI device also changes the registration ofits own device information (476).

Here, step 475 constitutes processing to add new storage to the diskdevice that is already present and under the management of the diskcontroller. The decision to add the storage is made according to thecapacity of the magnetic disks being managed by the disk controller.That is, the request to add the storage is made when the existing diskcapacity will not satisfy the write request from the host (when safetyfactors are also considered). Also, in addition to the current diskcapacity, the decision to add the storage can also be made according tothe I/O transaction number, transfer rate, control processor usage rateor other aspect of the performance of the disk controller itself. Thatis, a method is used in which the disk controller judges the decrease inthe I/O transaction number or the like and then yields the storagemanagement to the iSCSI devices, and the new storage is added.

Then, the storage broker 117 chooses the iSCSI device with the highestrank in the device list 118, and, according to this selection, the diskcontroller 110 performs iSCSI login and data access (480). The accessediSCSI device 160, 170 then performs normal iSCSI command processing(490). After that, the processing performed by the storage broker 117returns to 440, and the storage broker replying (micro) programs 165,175 return to 450.

Note that the disk controller can also perform deletion of theregistered iSCSI device as part of the normal processing. When theregistered iSCSI device breaks down, or the network performance of theiSCSI device deteriorates, the disk controller performs processing todelete the information for the corresponding iSCSI device from thedevice list and informs the iSCSI device that it has been cut off fromthe disk controller.

Thus, by performing the test registration and the testing via the routerand the network, the disk controller can obtain the information aboutthe devices connected on the network and the security information thatis obtained when each device is accessed, etc. Based on thisinformation, the devices are then ranked, which information is thenstored in the device list serving as the database. The optimum networkdevice can then be selected based on the rankings in the device list.Note that, in certain cases (such as when there is a request from theuser), the network device can be selected according to items other thanthe rankings.

FIG. 4 is a diagram showing a flowchart of registration, testing,updating and accessing by the storage broker device in accordance withEmbodiment 1. In FIG. 4, first, in response to the device registrationrequest from the host 100,101 or the SVP 130, the registration of theiSCSI device in the disk controller 110 (or, more specifically, in thestorage broker 117) is started (500). Next, the disk controller 110broadcasts the iSCSI device registration request on the network (510).The disk controller 110 registers the iSCSI device that replied into thedevice list 118 (515), and it assigns the rank within the registereddevice list 118 (520). The test access is then performed on theregistered device or the router 140 (535). Next, a check is performed todetermine whether or not the device list 118 needs to be updated (540).

If an update is necessary, then the disk controller 110 re-assigns theranks to the devices in accordance with the update information (545). Ifan update is not necessary, then an check is performed to determinewhether or not there is device list update information from an externallocation (550). If an update is necessary, then the ranks arere-assigned to the devices in accordance with the update information(555). If an update is not necessary, then a check is performed todetermine whether or not there are various types of device requests(560). If a device request has occurred, then a connection is made tothe iSCSI device with the highest rank and this device is registered(561). The processing at step 561 corresponds to the processing at step475 shown in FIG. 3, and the judgment to add the newly connected storageis made similar to that in step 475 in FIG. 3. Next, based on theoccurrence of the device request, iSCSI Login and data access are thenexecuted for the optimum device in the device list 118 (565). If thereis no request, or after the request processing is completed, then theprocedure returns to test access A at 535 (570).

FIG. 5 is a diagram showing a flowchart of iSCSI device registration,test reporting and a device list change, in accordance withEmbodiment 1. In FIG. 5, first, the iSCSI device starts iSCSI deviceprocessing (600). Next, the iSCSI device collects its own iSCSI deviceinformation and registration conditions (610). Next, the iSCSI devicechecks to determine whether or not there is a device list registrationrequest from the disk controller (615). If there is a registrationrequest, then the device information is registered into thecorresponding storage broker 117 in the disk controller. Next, the iSCSIdevice checks to determine whether or not a test access has beenperformed from an outside location (625). If access has been performed,then the iSCSI device replies to the storage broker 117 with the resultsof the access test (630). Furthermore, the iSCSI device checks todetermine whether or not the update list 118 needs to be updated (635).If an update is necessary, then the registered information is updated inthe corresponding storage broker 117 (640).

Next, the iSCSI device checks to determine whether the device has beenaccessed (645). If the device has been accessed, then normal iSCSIdevice target processing is performed (650). If the device has not beenaccessed, then the procedure returns to step 610 where the iSCSI devicecollects its own iSCSI device information and registration conditions.

FIG. 6 is a diagram showing an example of mirroring, backing up andsystem log data storage in accordance with Embodiment 1 of the diskcontroller. In FIG. 6, when mirroring is to be performed, data A 800 isstored as master data on the magnetic disk 120. On the other hand, dataA 850 is stored as slave data in the iSCSI heterogeneous storage 167 asthe data A 850. When this is performed, the data A 800 and the data A850 are synchronized.

When a backup is to be performed, data C 820 is stored as master data onthe magnetic disk 120. On the other hand, backup data is stored as olddata C 870 in the iSCSI heterogeneous storage 167. Furthermore, the diskcontroller records the storage system's access status. When an accidentoccurs, the old data C 870 from the backup data is used, and system logdata 880 for restoring the original data is stored onto a magnetic disk125 where broad capacity is available in the first place.

As explained above, when Embodiment 1 of the disk controller is used,wide-ranging storage connected to the IP network becomes usable, and thedesired storage capacity can be realized. Note that, Embodiment 1 wasexplained with respect to the construction in which the disk controllerhas the magnetic disk 120, which the disk controller manages directly.However, in the disk controller of Embodiment 1, the invention is basedon the fact that it can be connected over the network to the storage orthe magnetic disks. Therefore, the present invention is not restrictedto the construction explained above. A construction which does not havea directly managed magnetic disk naturally falls within the scope of thepresent invention as well. (This is also the same for Embodiment 2.)

FIG. 7 is a diagram showing an example of device registration, testing,updating and accessing between a disk controller and an iSCSI device inaccordance with Embodiment 2. In FIG. 7, first, a command to startdevice registration is sent to the disk controller 110 from one of thehosts 100, 101 or the SVP 130 (805). Next, device list registration isperformed according to an operation input from the SVP 130 or themanagement program 135 (800). Then, the disk controller 110 performs atest access to the iSCSI device or the router, obtains necessaryinformation, and transmits this to the SVP 130. Next, if there is achange in the iSCSI device information (such as a change in the capacityof an empty area) (855), the storage broker 117 assigns the device ranksin accordance with this update information (860), and then it transmitsthese rankings to the SVP.

In FIG. 7, all of the data to be written into the device list 118 isdisclosed from the SVP 130 (800, 840, 860). In other words, inEmbodiment 2, the SVP 130 gives instructions for the processing of step400 (the iSCSI device registration request), step 410 (the device's owninformation registration), and step 420 (the registration of the iSCSIdevice that replied into the device list), which are shown in FIG. 3.The subsequent data flow is similar to FIG. 3.

Thus, when Embodiment 2 is used, the procedures can proceed withoutspending time on registering and checking the devices. Furthermore, theranking of the registered iSCSI devices can also be performed by the SVP130, like the ranking performed by the control processor 115, asdescribed above. (See the description of ranking in connection withEmbodiment.)

As explained above, the disk controller of the present invention can besummarized as follows: In a conventional FC device heterogeneousconnection, iSCSI devices connected on a common IP network cannot beused to connect heterogeneous storage. Furthermore, when FCs are used tobuild a SAN, equipment costs become expensive; and, in a case wherecommon iSCSI devices are connected, it is difficult for the diskcontroller side to accurately learn the status of the devices, so thatthe heterogeneous connection could not be established easily. In orderto overcome these problems, in accordance with the present invention, adevice list is provided inside the disk controller in order to registerthe status of the externally connected IP network, the capacity of theiSCSI devices, the transfer rate, security, etc., and to assign theranks. Furthermore, at regular intervals the storage broker in the diskcontroller updates the various conditions. When the request is made forthe needed iSCSI device, the iSCSI device is connected based on thedevice list. Thus, it becomes possible to always select the optimumiSCSI device in terms of capacity, performance, security and cost. Italso becomes possible to establish the optimum heterogeneous storageconnection on the IP network.

In accordance with the present invention, the iSCSI I/F can be used tooptimally select from many heterogeneous storage entities existingexternally via the IP network. Therefore, the costs can be reduced andthe storage capacity can be expanded.

1. A disk control unit for controlling a magnetic disk which stores datafrom a computer comprising: a front end I/F which is an interface to thecomputer; a back end I/F which is an interface to the magnetic disk; aprocessor for controlling each section; and a main memory section,wherein the front end I/F and the back end I/F exchange information witha plurality of internet small computer system interface (iSCSI) devicesvia a network connected between the iSCSI devices and the front end andback end I/Fs, wherein each of the iSCSI devices manages a storage,wherein the main memory section stores registered information expressingan attribution of each of the iSCSI devices including capacityinformation indicating a capacity of the storage of each iSCSI device,access information indicating security and performance of each of theiSCSI devices through the network, and ranking information assigning arank to each of the iSCSI devices based on the registered informationand the access information, wherein the processor selects an appropriateiSCSI device according to various types of information including theranking information stored in the main memory section based on acondition as requested by the computer, wherein said capacityinformation of the storage of each iSCSI device is collected during;SCSI login processing to said iSCSI devices, and wherein said accessinformation indicating security and performance of each of the iSCSIdevices is collected at a timing of performing a test access to saidiSCSI devices.
 2. The disk control unit according to claim 1, whereincommunication with each of the iSCSI devices uses iSCSI protocol or IPprotocol.
 3. The disk control unit according to claim 1, wherein themain memory section is provided with a storage broker as a controlprogram for performing control on each of the iSCSI device each of whichmanages a storage, and is provided with a device list storing theregistered information, the access information, and the rankinginformation.
 4. The disk control unit according to claim 1, wherein theprocessor obtains the registered information from a replying programbuilt into each of the iSCSI devices, and obtains the access informationupon accessing each of the iSCSI devices via the network.
 5. The diskcontrol unit according to claim 4, wherein a service processor (SVP)with a built-in management program is connected to the processor,wherein the processor obtains the registered information and the accessinformation from terminal operations on the SVP, or from the managementprogram.
 6. The disk control unit according to claim 5, wherein theinformation exchange with each of the iSCSI devices is performed via thefront end I/F that can be connected to the computer.
 7. The disk controlunit according to claim 5, wherein the information exchange with each ofthe iSCSI devices is performed via the back end I/F that can beconnected to the magnetic disk being managed by the disk control unit.8. The disk control unit according to claim 1, wherein each storagemanaged by an iSCSI device has an iSCSI I/F.
 9. The disk control unitaccording to claim 4, wherein the processor obtains the registeredinformation and the access information via a router or a network switchconnected to the network.
 10. The disk control unit according to claim1, wherein the processor selects an iSCSI device to which to writemirrored data or backup data based on the registered information, theaccess information and the ranking information, in addition to themagnetic disk managed by the disk control unit.
 11. The disk controlunit according to claim 1, wherein the processor selects an iSCSI deviceto which to write log data accessed from the host based on theregistered information, the access information and the rankinginformation.
 12. A storage system comprising: a disk control unit; and adisk unit connected to the disk control unit which controls the diskunit to store data from a computer, wherein the disk control unitcomprises: a front end I/F which is an interface to the computer, a backend I/F which is an interface to the disk unit, a processor forcontrolling each section, and a main memory section, wherein the frontend I/F and the back end I/F provided to the disk control unit areconnected to a plurality of internet small computer system interface(iSCSI) devices via a network connected between the iSCSI devices andthe front end and back end I/Fs, wherein each of the iSCSI devicesmanages a storage, wherein the main memory section inside the diskcontrol unit stores registered information expressing an attribution ofeach of the iSCSI devices including capacity information indicating acapacity of the storage of each iSCSI device, access informationindicating security and performance of each of the iSCSI devices throughthe network, and ranking information assigning a rank to each of theiSCSI devices based on the registered information and the accessinformation, wherein the disk control unit selects an appropriate iSCSIdevice according to various types of information including the rankinginformation stored in the main memory section, based on a condition asrequested by the computer, wherein said capacity information of thestorage of each iSCSI device is collected during iSCSI login processingto said iSCSI devices, and wherein said access information indicatingsecurity and performance of each of the iSCSI devices is collected at atiming of performing a test access to said iSCSI devices.
 13. Thestorage system according to claim 12, wherein the communication witheach of the iSCSI devices uses iSCSI protocol or IP protocol.
 14. Thestorage system according to claim 12, wherein the processor obtains theregistered information from a replying program built into each of theiSCSI devices, and obtains the access information upon accessing each ofthe iSCSI devices via the network.
 15. The storage system according toclaim 14, wherein the disk control unit is connected to a ServiceProcessor (SVP), wherein the processor obtains the registeredinformation and the access information from terminal operations on theSVP, or from a management program executed by the SVP.
 16. A storagesystem comprising: a disk control unit; and a disk unit connected to thedisk control unit which controls the disk unit to store data from acomputer, wherein the disk control unit comprises: a front end I/F whichis an interface to the computer, a back end I/F which is an interface tothe disk unit, a processor for controlling each section, and a mainmemory section, wherein the front end I/F and the back end I/F providedto the disk control unit are connected to a plurality of internet smallcomputer system interface (iSCSI) devices via a network connectedbetween the iSCSI devices and the front end and back end I/Fs, whereineach of the iSCSI devices manages a storage, wherein the main memorysection stores, as a device list, registered information expressing anattribution of each of the iSCSI devices including capacity informationindicating a capacity of the storage of each iSCSI device, accessinformation indicating security and performance of each of the iSCSIdevices obtained upon accessing each of the iSCSI devices via thenetwork, and ranking information assigning a rank to each of the iSCSIdevices based on the registered information and the access information,wherein the main memory section further stores a control program forperforming control on each of the iSCSI devices as a storage broker,wherein an appropriate iSCSI device is selected from the device listincluding the ranking information stored in the main memory section,based on a condition as requested by the computer, wherein said capacityinformation of the storage of each iSCSI device is collected duringiSCSI login processing to said iSCSI devices, and wherein said accessinformation indicating security and performance of each of the iSCSIdevices is collected at a timing of performing a test access to saidiSCSI devices.
 17. A disk control unit according to claim 1, furthercomprising: a plurality of said front end I/Fs each of which is aninterface to one of a plurality of computers; a plurality of said backend I/Fs each of which is an interface to one of a plurality of magneticdisks, wherein each front end I/F and each back end I/F exchangesinformation with said iSCSI devices via the network connected betweenthe iSCSI devices and the front end and back end I/Fs.
 18. A storagesystem according to claim 12, further comprising: a plurality of saidfront end I/Fs each of which is an interface to one of a plurality ofcomputers; a plurality of said back end I/Fs each of which is aninterface to one of a plurality of magnetic disks, wherein each frontend I/F and each back end I/F exchanges information with said iSCSIdevices via the network connected between the iSCSI devices and thefront end and back end I/Fs.
 19. A storage system according to claim 16,further comprising: a plurality of said front end I/Fs each of which isan interface to one of a plurality of computers; a plurality of saidback end I/Fs each of which is an interface to one of a plurality ofmagnetic disks, wherein each front end I/F and each back end I/Fexchanges information with said iSCSI devices via the network connectedbetween the iSCSI devices and the front end and back end I/Fs.
 20. Adisk control unit according to claim 1, wherein said processordetermines, upon receipt of a write request, whether a capacity of astorage of an iSCSI device being used satisfies the write request, andwherein said processor requests the iSCSI device being used to addstorage if the capacity of the storage of the iSCSI device being useddoes not satisfy the write request.
 21. A storage system according toclaim 12, wherein said processor determines, upon receipt of a writerequest, whether a capacity of a storage of an iSCSI device being usedsatisfies the write request, and wherein said processor requests theiSCSI device being used to add storage if the capacity of the storage ofthe iSCSI device being used does not satisfy the write request.
 22. Astorage system according to claim 16, wherein said processor determines,upon receipt of a write request, whether a capacity of a storage of aniSCSI device being used satisfies the write request, and wherein saidprocessor requests the iSCSI device being used to add storage if thecapacity of the storage of the iSCSI device being used does not satisfythe write request.